Use of flow-injection sample-to-standard addition methods for quantification of metals leached by selective chemical extraction from sewage sludge Original Research Article

The flow injection sample-to-standard addition method (FI-SAM) proposed by Israel and Barnes and a modification of it was employed for determination of the extractable contents of chromium, lead, nickel and zinc in a sewage sludge sample obtained from an urban wastewater processing plant. The new calibration method was a modification of the one established by Israel and Barnes in which the sample was injected into a blank solution and two different standard solutions. The advantages of this modified calibration method were: (i) sample consumption was minimised in comparison with the `reverseʹ flow injection method since the sample was not used as carrier; (ii) a blank that was matrix matched to the sample was not required; (iii) a similar precision was observed in comparison with the original procedure. For studying FI-SAM calibration strategies, extractable metals obtained by using two known sequential extraction schemes (Tessier and BCR) were determined. Only fractions that required calibration with the standard addition method for metal determination were considered. FI-SAMs compensate for interference effects caused by concomittants co-extracted at each stage of the sequential extraction scheme from sewage sludge, for all metals studied except for chromium.